Reduced Plant Diversity Research Articles

Arbuscular mycorrhizal fungi alleviate the negative effects of increases in phosphorus (P) resource diversity on plant community structure by improving P resource utilization

Nutrient resource utilization is essential for plant community composition and productivity. Previous studies found that an increase in resource diversity causes species losses and reduces plant diversity. Arbuscular mycorrhizal (AM) fungi can increase plant productivity and nutrient uptake, however, whether AM fungi can reduce the negative influence of nutrient resource diversity on plant composition is still not well understood. A microcosm experiment was conducted with four phosphorus (P) sources (at five levels of P resource diversity) and two AM fungal species, and the plant community composition, aboveground biomass, and P content were measured and calculated. Plant species diversity and richness decreased with increasing soil P resource diversity in the absence of AM fungi, while the decrease was less when AM fungi were present. The biomass and P content of the aboveground plants increased with increasing AM fungal diversity and soil P resource diversity. The results of a structural equation model suggest that AM fungi could reduce the negative effects of increasing P resource diversity on plant community composition by improving plant density and P uptake. Our results indicate that AM fungi can maintain higher plant species diversity and increase plant productivity by increasing P resource utilization efficiency.

Increasing effects of chronic nutrient enrichment on plant diversity loss and ecosystem productivity over time.

Human activities are enriching many of Earth's ecosystems with biologically limiting mineral nutrients such as nitrogen (N) and phosphorus (P). In grasslands, this enrichment generally reduces plant diversity and increases productivity. The widely demonstrated positive effect of diversity on productivity suggests a potential negative feedback, whereby nutrient-induced declines in diversity reduce the initial gains in productivity arising from nutrient enrichment. In addition, plant productivity and diversity can be inhibited by accumulations of dead biomass, which may be altered by nutrient enrichment. Over longer time frames, nutrient addition may increase soil fertility by increasing soil organic matter and nutrient pools. We examined the effects of 5-11yr of nutrient addition at 47 grasslands in 12 countries. Nutrient enrichment increased aboveground live biomass and reduced plant diversity at nearly all sites, and these effects became stronger over time. We did not find evidence that nutrient-induced losses of diversity reduced the positive effects of nutrients on biomass; however, nutrient effects on live biomass increased more slowly at sites where litter was also increasing, regardless of plant diversity. This work suggests that short-term experiments may underestimate the long-term nutrient enrichment effects on global grassland ecosystems.

荒漠草原植物多样性恢复与土壤生境的关系

为揭示荒漠草原围栏封育后植物多样性的恢复对土壤生境的响应机制，以围栏封育和适度放牧草地的灰钙土和风沙土生境植物群落为研究对象，采用方差分析和冗余分析（redundancy analysis RDA）方法，研究了围栏封育后植物多样性的变化及其与土壤生境物理和化学因子的关系。结果表明：（1）相对于适度放牧利用，围栏封育显著降低了灰钙土和风沙土生境植物多样性；随着封育年限的增加，植物多样性呈现显著，且封育的负效应随着封育年限的增加而增加；（2）两种土壤生境下植物多样性与生物量均表现为负相关。植物群落对灰钙土和风沙土两种土壤生境下表现出的不同点有：（1）灰钙土生境下，植物多样性与砂粒正相关，生物量与有机碳，全氮正相关；（2）风沙土生境下，植物多样性与有机碳，全氮正相关，生物量与电导率正相关。未来荒漠草原退化草地植物多样性恢复需要充分考虑不同土壤生境类型的影响，草地管理需要采取适度利用和封育保护相结合道路。;In order to reveal the response mechanism of plant diversity restoration to soil habitat after fencing in desert steppe, the plant communities in sierozem soil and aeolian sandy soil habitats of fenced and moderately grazed grassland were selected as the research objects. The variance analysis and redundancy analysis (RDA)were used to study the changes of plant diversity after enclosure and its relationship with physical and chemical factors of soil habitat. The results showed that:(1) compared with moderate grazing, enclosure significantly reduced plant diversity in sierozem soil and aeolian sandy soil. With the increase of enclosure years, plant diversity was significant, and the negative effect of enclosure increased with the increase of enclosure years. (2) There was a negative correlation between plant diversity and biomass in both soil habitats. The differences of plant communities between sierozem soil and aeolian sandy soil were as follows:(1) In sierozem soil, plant diversity was positively correlated with sand, while biomass was positively correlated with organic carbon and total nitrogen. (2) In aeolian sandy soil, plant diversity was positively correlated with organic carbon and total nitrogen, as well as biomass was positively correlated with electrical conductivity. In conclusion, the effects of different soil habitat types should be fully considered in the restoration of plant diversity of the degraded grassland in desert steppe in the future.

Effects of mowing and fertilization on soil quality in a semiarid grassland of North China

AbstractSoil quality has been defined as the capacity to sustain biological productivity and maintain environmental quality. Mowing and fertilization may affect ecosystem function through numerous soil properties, especially in semiarid grasslands where plant growth is limited by nutrient availability. However, the effects of grassland management on the trade‐off between soil quality and plant community structure is still unclear. Understanding the effect of land use type on soil quality is essential to adopt proper grassland management practices for a specific region. Principal component analysis was used to calculate a soil quality index (SQI) with 18 variables under the following treatments: control, mowing, nitrogen addition, and mowing plus nitrogen addition in August 2017 in a typical steppe of North China. This study showed that nitrogen addition significantly increased SQI by 0.82, field water capacity by 3.77%, soil capillary porosity by 3.30%, and soil available nitrogen content by 13.85 mg kg−1, but reduced soil aggregate proportion by 3.07%, microbial biomass nitrogen content by 7.74 mg kg−1, arbuscular mycorrhizal fungi by 0.02 μmol g−1, the ratio of fungus to bacteria by 0.16, and the ratio of Gram‐positive bacteria to Gram‐negative bacteria by 0.13 across the mowing and unmowing treatments. Nitrogen addition could improve productivity by increasing the soil quality but reduce plant diversity of the grassland ecosystems. Mowing did not affect SQI and aboveground biomass. The results suggested that fertilization as grassland management improved soil quality and productivity, whereas mowing was a sustainable way to maintain plant diversity in this semiarid grassland.

Symbiotic soil fungi enhance resistance and resilience of an experimental grassland to drought and nitrogen deposition

Abstract Ecosystem stability is threatened by multiple global change factors such as drought and elevated nitrogen deposition. Yet, it is still poorly understood whether soil organisms can buffer against such perturbations. Here we focus on arbuscular mycorrhizal fungi (AMF), a common and widespread group of soil fungi. AMF form symbiotic associations with the majority of terrestrial land plants and promote a range of ecosystem services including plant production, diversity and nutrient cycling. We tested whether AMF have the ability to enhance the resistance and resilience of plant communities under soil moisture deficit (hereby drought) and nitrogen deposition. Grassland microcosms with 11 different plant species were established with and without AMF and exposed to elevated nitrogen levels and to an intermittent period of drought. Drought strongly reduced plant productivity and nitrogen cycling, but had limited effects on plant diversity. Nitrogen enrichment reduced plant diversity and increased nitrogen leaching and N2O emissions. The presence of AMF enhanced plant productivity, plant diversity and reduced nitrogen losses. AMF facilitated the resistance of plant productivity and nitrogen cycling to drought and the recovery of the plant community structure back to its pre drought state. Furthermore, AMF also mitigated the adverse effects of nitrogen enrichment on the resistance of multiple ecosystem functions to drought. Synthesis. Our work highlights the integral role of AMF for the stability of ecosystem functioning; AMF are not only able to promote resistance to harsh conditions of global change but also improve resilience by enabling plant communities to recover. These findings underline AMF's insurance capacity to buffer ecosystems against global change.

Terrestrial organic carbon isotopic composition (δ13Corg) and environmental perturbations linked to Early Jurassic volcanism: Evidence from the Qinghai-Tibet Plateau of China

Abstract The Early Jurassic break-up of Pangea and the formation of the Central Atlantic Ocean are associated with changes to the atmosphere, climate, and environment, as recorded in marine carbonates from the western Tethys Ocean. However, the expression of these global changes in terrestrial successions is less well known. To better understand terrestrial-response, we investigated organic carbon isotope composition (δ13Corg), weathering trends and geochemistry in Lower Jurassic lacustrine strata in the Qaidam Basin, China, on the northern margin of the eastern Tethys Ocean. Four negative δ13Corg carbon isotope excursions are identified in lacustrine black shales during the Pliensbachian to early Toarcian stages. These negative excursions correspond to the early Pliensbachian Warming Interval, the Subnodonus Negative Event at the beginning of the late Pliensbachian, the Pliensbachian–Toarcian Boundary Event, and the early Toarcian Oceanic Anoxia Event (T-OAE), respectively, well documented in western Tethys Ocean successions. In our terrestrial successions from the Qaidam Basin, the first three events occurred under relatively warm and humid climates associated with enhanced weathering, lake transgression, and the prevalence of swamp environments. In contrast, the T-OAE was a period of intense warming and arid climate, expressed by the deposition of red beds, a hiatus in coal deposition, a sharp reduction in plant diversity, and a floristic turnover in palynoflora. Our findings show that each negative excursion is associated with peaks in mercury and nickel concentrations, supporting the hypothesis that magma intrusion into organic-rich rocks and accompanying the volcanic eruption was responsible.

Fast and furious: Early differences in growth rate drive short-term plant dominance and exclusion under eutrophication.

The reduction of plant diversity following eutrophication threatens many ecosystems worldwide. Yet, the mechanisms by which species are lost following nutrient enrichment are still not completely understood, nor are the details of when such mechanisms act during the growing season, which hampers understanding and the development of mitigation strategies.Using a common garden competition experiment, we found that early‐season differences in growth rates among five perennial grass species measured in monoculture predicted short‐term competitive dominance in pairwise combinations and that the proportion of variance explained was particularly greater under a fertilization treatment.We also examined the role of early‐season growth rate in determining the outcome of competition along an experimental nutrient gradient in an alpine meadow. Early differences in growth rate between species predicted short‐term competitive dominance under both ambient and fertilized conditions and competitive exclusion under fertilized conditions.The results of these two studies suggest that plant species growing faster during the early stage of the growing season gain a competitive advantage over species that initially grow more slowly, and that this advantage is magnified under fertilization. This finding is consistent with the theory of asymmetric competition for light in which fast‐growing species can intercept incident light and hence outcompete and exclude slower‐growing (and hence shorter) species. We predict that the current chronic nutrient inputs into many terrestrial ecosystems worldwide will reduce plant diversity and maintain a low biodiversity state by continuously favoring fast‐growing species. Biodiversity management strategies should focus on controlling nutrient inputs and reducing the growth of fast‐growing species early in the season.

Resource enrichment combined with biomass removal maintains plant diversity and community stability in a long-term grazed grassland

Abstract Aims Long-term heavy grazing reduces plant diversity and ecosystem function by intensifying nitrogen (N) and water limitation. In contrast, the absence of biomass removal can cause species loss by elevating light competition and weakening community stability, which is exacerbated by N and water enrichment. Hence, how to maintain species diversity and community stability is still a huge challenge for sustainable management of worldwide grasslands. Methods We conducted a 4-year manipulated experiment in six long-term grazing blocks to explore combination of resource additions and biomass removal (increased water, N and light availability) on species richness and community stability in semiarid grasslands of Inner Mongolia, China. Important Findings In all blocks treated with the combination of resource additions and biomass removal, primary productivity increased and species richness and community stability were maintained over 4 years of experiment. At both species and plant functional group (PFG) levels, the aboveground biomass of treated plants remained temporally stable in treatments with the combination of N and/or water addition and biomass removal. The maintenance of species richness was primarily caused by the biomass removal, which could increase the amount of light exposure for grasses under resource enrichment. Both species asynchrony and stability of PFGs contributed to the high temporal stability observed in these communities. Our results indicate that management practices of combined resource enrichment with biomass removal, such as grazing or mowing, could not only enhance primary productivity but also maintain plant species diversity, species asynchrony and community stability. Furthermore, as overgrazing-induced degradation and resource enrichment-induced biodiversity loss continue to be major problems worldwide, our findings have important implications for adaptive management in semiarid grasslands and beyond.

A Multi-Scale Approach to Predict the Fractional Cover of Medusahead (Taeniatherum Caput-Medusae)

Medusahead is an aggressive, winter annual that is of dire concern for the health and sustainability of western rangelands in the United States. Medusahead reduces plant diversity, alters ecosystem function, and reduces carrying capacities for both livestock and wildlife. The species has competitive advantages over cheatgrass and native grasses that causes an increased amount of fine fuels deposited on western rangelands. The Channeled Scablands of eastern Washington in the United States represent a typical example of a region being challenged by the expansion of this weed. The costs of the invasion are high and financial constraints can limit successful management. Managers need the ability to identify medusahead across entire landscapes, so they can work towards effective and efficient management approaches. Remote sensing offers the ability to measure vegetation cover at large spatial scales, which can lead to a better understanding of the invasive characteristics of problematic species like medusahead. For instance, research has been successful in creating large-scale distribution maps of cheatgrass over western rangelands. Many applications rely on the phenological characteristics of a target plant which can present problems in separating two species with similar phenologies (i.e. cheatgrass & medusahead). A medusahead-specific map gives managers the flexibility to prioritize and direct management needs when attempting to control the spread of medusahead into non-invaded areas. This study integrated GPS acquired field locations from three study sites (Sites S, C, & N) and imagery from two remote sensing platforms (1-m aerial imagery & 30-m Landsat), to model and predict fractional cover of medusahead over 37,000+ ha of rangelands in the Channeled Scabland region of eastern Washington. Using a multi-scaled approach, this research showed that regression tree algorithms can model the complex spectral response of senesced medusahead using late summer Landsat scenes. The predictive performances resulted in a R2 of 0.80 near the model's training site (Site S) and an average R2 of 0.68 away from the training site (Sites C & N). This research provides a non-phenological approach to produce accurate large-scale, distribution maps of medusahead which can aid land managers who are challenged by its invasion.

Decomposition disentangled: A test of the multiple mechanisms by which nitrogen enrichment alters litter decomposition

AbstractNitrogen (N) enrichment has direct effects on ecosystem functioning by altering soil abiotic conditions and indirect effects by reducing plant diversity and shifting plant functional composition from dominance by slow to fast growing species. Litter decomposition is a key ecosystem function and is affected by N enrichment either by a change in litter quality (the recalcitrance of the plant material) or through a change in soil quality (the abiotic and biotic components of the soil that affect decomposition). How the direct and indirect effects of N alter soil and litter quality remains poorly known.We designed a large grassland field experiment manipulating N enrichment, plant species richness and functional composition in a full factorial design. We used three complementary litterbag experiments, combined in a structural equation model (SEM), to quantify the effects of the treatments and various measures of functional composition and diversity on litter and soil quality and overall decomposition.Our results revealed multiple drivers of litter quality and showed that nutrient concentrations (N and calcium) were about twice as important as structural components (leaf dry matter content, fibres) in determining litter quality. Overall the experimental results suggest that N enrichment increases litter decomposition mostly indirectly through a shift in functional composition toward faster growing plant species, producing higher quality litter. N enrichment also altered soil quality and thereby litter decomposition, through its effects on vegetation cover.Our approach provides a mechanistic tool to test the drivers of litter decomposition across different ecosystems. Our results show that litter quality is determined by several nutrient and structure traits and highlight the importance of considering shifts in plant species composition when assessing the effects of N enrichment on decomposition.

For a few years more: reductions in plant diversity 70 years after the last fire in Mediterranean forests

Changes in community diversity and dynamics after fires in Mediterranean ecosystems are rarely investigated more than a few years after the fire even though pronounced changes can be expected in the longer term due to substitution of canopy species. Pinus halepensis is strongly promoted by wildfire and should therefore be gradually substituted by Quercus species as the time since the last fire increases. We hypothesized that this tree substitution would cause changes in understorey plant diversity by changing resource availability and the abundance and properties of woody debris, leading to changes in biogeochemical processes. To test this hypothesis, we investigated the effect of the time since last fire on vascular plant composition and diversity by studying a 130 years post-fire chronosequence in mixed Mediterranean forests. The canopy composition went from domination by Pinus halepensis to domination by Quercus 70 years after the most recent fire. This transformation was associated with a change in the understorey involving a rarefaction of species present during the first decades after the fire. The plant density or cover also changed with time since the last fire, indicating a succession driven by species rarefaction rather than substitution. The mean richness and Shannon diversity per quadrat were highest shortly after the fire, and were significantly lower 70 or more years after the last fire. Fires are important for supporting highly diversified fire-dependent plant communities, and total plant richness decreases monotonically over time after fires, suggesting that fire suppression may reduce diversity in Mediterranean forests.

Land-use intensity indirectly affects soil multifunctionality via a cascade effect of plant diversity on soil bacterial diversity

Land-use intensification impairs multiple soil ecosystem functions and services (hereafter ‘soil multifunctionality’; SMF) crucial to human wellbeing by influencing plant diversity and soil microbial communities. However, available information is limited on the contrasting and interaction effects of plant diversity and soil microbial communities on SMF under a gradient of land-use intensity (LUI). We measured five soil ecosystem functions associated with effective soil nutrients and water retention along 15 LUI gradients on Hainan Island, where land-use change and biodiversity loss has been severe. We used phospholipid fatty acid (PLFA) method to determine the diversity and composition of soil microbial communities. The relationships among LUI, plant diversity (species and functional diversity), soil microbial diversity (bacterial and eukaryotic diversity), and soil microbial composition (fungi/bacteria and Gram-positive/Gram-negative bacteria ratios), and SMF were examined. The LUI affected SMF indirectly by reducing plant diversity and its interaction with soil bacterial diversity. Specifically, with increase in LUI, loss of plant species diversity indirectly reduced SMF via reduction of soil bacterial diversity. In contrast, loss of tree height diversity reduced SMF directly and indirectly through decrease in soil bacterial diversity. Importantly, the indirect effect of LUI mediated by tree height diversity was stronger than that mediated by plant species diversity and soil bacterial diversity. These results provide evidence that the cascade effect of plant diversity to soil bacterial diversity mediates the impacts of land-use intensity on soil multifunctionality, and further suggest that focusing on tree height diversity may be helpful for sustainable ecosystem management and predicting the impacts of land use changes.

Declines in native forb richness of an imperiled plant community across an anthropogenic nitrogen deposition gradient

AbstractAnthropogenic nitrogen (N) deposition is known to reduce plant diversity in ecosystems worldwide; however, effects on the diversity of Mediterranean‐type ecosystems—global hotspots of biodiversity—are relatively unexplored. In California, elevated N deposition due to air pollution has a multitude of ecological effects including the facilitation of nonnative plant invasion and altered ecosystem functioning, but impacts on plant richness have been inadequately quantified. We addressed this research gap by evaluating patterns of plant richness in coastal sage scrub (CSS), a severely threatened, highly diverse Mediterranean‐type shrubland, across the Santa Monica Mountains National Recreation Area. This is the largest urban national park in the United States and experiences a strong gradient of N deposition due to its proximity to urban Los Angeles. We measured soil N, plant cover, and richness at 30 CSS sites across this gradient and used regression analyses to explore relationships between richness, N deposition, and other environmental variables. We observed significant declines in plant richness across a steep gradient of soil N availability that paralleled patterns of N deposition, primarily due to decreases in native forb species. Our analyses identified soil N as the best predictor of patterns of native forb richness, but other factors, including nonnative plant cover and aridity, may also drive reduced richness. In addition to the marked decline in the number of native forb species, increasing N deposition was also associated with lower native shrub richness per area and increased cover of nonnatives. These results highlight the threat posed by N deposition to the conservation of this already imperiled ecosystem under continued environmental change.

An Emergy-Based Approach to Assess and Valuate Ecosystem Services of Tropical Wetland Pastures in Brazil

Wetland grasslands are important ecosystems for raising beef cattle, because they are highly productive and present forages with high quality. Most of these ecosystems are threatened by overgrazing or by being replaced by exotic pastures. Emergy synthesis approach was used to assess and value the services provided by native pastures wetland under three conservation status and also to compare them to exotic pastures on wetlands. The ecosystem service that was assessed included forage provision for calves production estimated from grazing capacity of cow with calf at the foot. Habitat maintenance to plant diversity and wild herbivores were also evaluated. The results showed that natural wetland pastures with better conservation status provided valuable ecosystem services and are highly renewable. Data envelopment analysis (DEA) showed that regardless of the conservation state of the natural pastures, wet native grasslands were more efficient than wet exotic grasslands. Replacing native pastures by exotic ones may reduce plant diversity and the renewability of the system. The proposed method has a holistic approach to pasture ecosystems and is able to help decision-makers to define sustainable management practices and to subsidise public policies when it comes to payments regarding ecosystem services.

Tecnologías agroforestales para una Selva Baja Caducifolia: propuesta metodológica

El diseño e implementación de tecnologías agroforestales presenta diversos problemas, debido a la complejidad de las mismas y a la falta de paquetes de tecnología en México. El objetivo de este trabajo fue proponer una metodología de evaluación de tierras, para diseñar tecnologías agroforestales en el ejido Ajuchitlán, Tlaquiltenango, Morelos. El método consistió en el diagnóstico de los aspectos biofísicos y agroforestales para definir unidades básicas relativamente homogéneas (UP), identificar las especies más representativas y detectar las principales limitantes. Se realizaron entrevistas semiestructuradas a los productores para conocer otras restricciones, determinar su principal interés económico y seleccionar las especies arbóreas y arbustivas preferidas para el diseño de las tecnologías agroforestales, así como evaluar la viabilidad económica de las mismas. La vegetación secundaria de selva baja caducifolia en sus diferentes densidades, condiciones climáticas y fisiográficas fue la unidad del paisaje (UP) que representó el uso con mayor superficie en la región. Las limitantes detectadas fueron: cercado en las zonas agrícolas y de pastizal, degradación del suelo en la parte alta del área de estudio y disminución de la diversidad vegetal en las unidades de tierra con baja densidad arbórea. Las tecnologías agroforestales propuestas fueron cercas vivas en la zona agrícola-ganadera, barreras vivas en la parte alta y enriquecimiento de acahuales en la unidad de tierra con baja densidad arbórea. El buen manejo silvícola de las tecnologías sugeridas puede incrementar los ingresos económicos de los agricultores, principalmente, por la venta de leña. Esta investigación contribuye a obtener información local de la zona.

Garlic mustard (Alliaria petiolata) is associated with an overall reduction in plant diversity, but is more likely to co-exist with native than alien species

ABSTRACTBackground: Alliaria petiolata (garlic mustard) is a widespread allelopathic invasive species in North America, but despite extensive research we do not fully understand how it impacts plant communities.Aims: We tested the hypothesis that A. petiolata facilitates the introduction of additional alien species as predicted by the invasional meltdown hypothesis.Methods: We conducted co-occurrence surveys to compare the numbers of alien and native species in communities surrounding A. petiolata plants with those surrounding an allelopathic native species. We also conducted an experiment to compare recruitment of native and alien species in pots dominated by either A. petiolata or a native species.Results: A. petiolata plots in the co-occurrence surveys had relatively high proportions of bare ground, suggesting habitat modification, plus lower species richness and disproportionately fewer alien species. There was a greater tendency for native species than alien species to establish in A. petiolata pots.Conclusions: A. petiolata does not promote additional alien species, and in fact may be a more effective competitor against alien than native species in North America. This could help explain its invasive success in disturbed habitats, and illustrates the need to consider separately alien and native species when assessing the outcomes of competition.

Insect and plant traits drive local and landscape effects on herbivory in grassland fragments

AbstractHerbivory is one of the most important antagonistic insect–plant interactions and can be influenced by factors at local and landscape scales. Landscape fragmentation may reduce herbivory directly (i.e., decreasing abundance and species richness of herbivores), but also indirectly increase herbivory (i.e., releasing herbivores from top‐down control). At a local scale, reduced plant diversity may enhance herbivory through lessened associated resistance, while resource availability (i.e., higher vegetation height and cover) may promote herbivory. Few studies have simultaneously considered the influence of local and landscape variables on insect herbivory. We evaluate effects of landscape (fragment size, connectivity, and arable land percentage) and local factors (plant cover and height and plant species richness) on insect herbivory in fragmented calcareous grasslands. Further, we ask whether these effects depend on feeding traits of herbivores (chewers vs. suckers) and habitat specialization of plants (specialists vs. generalists). Results show that herbivory was best explained by models including variables at both local and landscape scales. However, local factors were more important than landscape variables. Herbivory was in all cases positively related to height of herbs (i.e., taller and more heterogeneous food resources), whereas the effect of plant species richness varied with feeding traits of herbivores. Herbivory by chewers, which are commonly more generalist feeders, was negatively affected by plant species richness, supporting the idea of associated plant resistance. In contrast, herbivory by suckers, which tend to be more specialized, increased with plant richness. Although there was little influence of landscape scale, herbivory on specialist plants was significantly higher in smaller grasslands probably as a consequence of herbivore release from natural enemies. Functional redundancy among herbivore species would allow to maintain overall herbivory in fragmented calcareous grasslands. This study highlights the need to consider different herbivore and plant traits for a better understanding of herbivory responses to local and landscape factors.

Diversity of arbuscular mycorrhizal fungi and nematodes in a 14 years no-tillage chronosequence

We evaluated the effects of the conversion of native areas of the Cerrado to no-tillage on the population of arbuscular mycorrhizal fungi and nematodes. Three areas under no-tillage (7, 11 and 14 years of cultivation) were evaluated and compared to adjacent areas of the Cerrado not impacted by agriculture. Results indicated that although no-tillage is a conservation system, it has either slightly reduced, slightly improved, or maintained the taxonomic and functional diversity of arbuscular mycorrhizal fungi and nematodes, even after 14 years of cultivation. In addition, cultivated areas presented reduced diversity of arbuscular mycorrhizal fungi, and increased occurrence of plant parasitic nematodes. The observed differences could be a result of both disturbance to the soil structure through agriculture and reduced plant diversity in the soybean-corn rotation, as compared to the adjacent uncultivated Cerrado.

Repeated fires reduce plant diversity in low‐elevation Wyoming big sagebrush ecosystems (1984–2014)

AbstractSagebrush is one of the most imperiled ecosystems in western North America, having lost about half of its original 62 million hectare extent. Annual grass invasions are known to be increasing wildfire occurrence and burned area, but the lasting effects (greater than five years post‐fire) that the resulting reburns have on these plant communities are unclear. We created a fire history atlas from 31 yr (1984–2014) of Landsat‐derived fire data to sample along a fire frequency gradient (zero to three fires) in an area of northern Nevada that has experienced frequent fire in this time period. Thirty‐two percent of our study area (13,000 km2) burned in large fires (over 404 ha) at least once, 7% burned twice, and 2% burned three or more times. We collected plant abundance data at 28 plots (N = 7 per fire frequency), with an average time since fire of 17 yr. We examined fire's effect on plant diversity using species accumulation curves, alpha diversity (Shannon's dominance, Pielou's evenness, and number of species), and beta diversity (Whittaker, Simpson, and Z indexes). For composition, we used non‐metric multidimensional scaling. We then used PERMANOVA models to examine how disturbance history, temperature, precipitation, and aridity around the time of the fire affected subsequent community composition and diversity. One fire fundamentally changed community composition and reduced species richness, and each subsequent fire reduced richness further. Alpha diversity decreased after one fire. Beta diversity declined after the third fire. Cover of exotics was 10% higher in all burned plots, and native cover was 20% lower than in unburned plots, regardless of frequency. PERMANOVA models showed fire frequency and antecedent precipitation as the strongest predictors of beta diversity, while time since fire and vapor pressure deficit for the year of the fire were the strongest predictors of community composition. Given that a single fire has such a marked effect on species composition, and repeated fires reduce richness and beta diversity, we suggest that in lower elevation big sagebrush systems fire should be minimized as much as possible, perhaps even prescribed fire. Restoration efforts should be focused on timing with wet years on cooler, wetter sites.

A focus on the European hamster to illustrate how to monitor endangered species.

Agriculture intensification, marked by the generalization of crop monoculture, by the increase in plot size and by the reduction of plant diversity, has led to huge decline in wildlife in European farmlands. In such habitat, research has long been biased towards birds and invertebrates, while very few studies have investigated the effect on small mammals. Considering the European hamster, Cricetus cricetus, we therefore review the different techniques that can be used to investigate the impact of environmental changes and conservation measures in small and endangered wild mammals. We suggest that only a multidisciplinary approach will allow exploration of these effects, combining experimental laboratory work on captive-bred animals with the monitoring of wild individuals. In particular, individual energy balance has to be investigated and measured as accurately as possible, through either biochemical or bio-logging techniques. It is, indeed, the most affected physiological trait in a changing environment, as it determines both the reproductive output and the survival of the individual. We also discuss the inconvenience of capture-release approaches for such an endangered species and emphasize the disturbance that experimental protocols could impose on the hamster.